Intersymbol interference (ISI) is a form of distortion of a digital signal transmitted across a serial link in which one symbol interferes with subsequent symbols causing the symbols to “blur” together. ISI may have an effect similar to noise.
A serial link may include a serial transmitter, a channel, and a serial receiver. ISI may be caused, for example, by a channel with a non-ideal frequency response, e.g., a channel that attenuates high-frequency components of a signal more than low-frequency components, or delays the phase of some frequency components more than others. Other elements in a serial link may also cause ISI.
The presence of ISI in a system may introduce errors in a decision device such as a slicer at the receiver output. One approach for reducing the effects of ISI involves the use of one or more filters that compensate or partially compensate for the frequency response of the channel, so that the frequency response of the cascade of the channel and the one or more filters is ideal or more nearly ideal than the channel. In the design of such (transmitting and receiving) filters, an objective may be to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible.
A continuous-time linear equalizer (CTLE) may be used as a part of the analog front end of a receiver to cancel the part of the system ISI introduced by a channel. A CTLE may be an analog circuit, which may have a large number of possible configurations; each configuration produces a different circuit behavior, e.g., a different frequency response. Of these configurations it may be that only a small subset (e.g., one) minimizes ISI, and results in a lower error rate for the link.
Some or all aspects of a CTLE may be hard-wired, e.g., they may be controlled by component values selected at design time and fabricated as part of the fabrication of an integrated circuit. In such a case, the CTLE configuration expected to provide the best performance may be identified by trial and error in simulation. For example, a time-domain simulation may be run repeatedly over a large set of CTLE configurations, and the configuration that produces the best performance may be selected. Such an approach may be costly and time consuming. Thus, there is a need for efficient systems and or methods for identifying CTLE configurations expected to provide good performance in a link with ISI.